1. Field of the Invention
The present invention generally relates to a method for producing a ceramic body, and more particularly, relates to, a method for producing, for example, a chip-type ceramic electronic component such as a laminated ceramic capacitor.
2. Description of the Related Art
Conventionally, a laminated ceramic capacitor as an example of a ceramic body is produced in the following way.
First, a slurry is prepared which contains a ceramic raw material powder. This slurry is formed into sheets to prepare ceramic green sheets. A conductive paste as a raw material for internal electrode layers is applied onto surfaces of the ceramic green sheets in accordance with a predetermined pattern. This conductive paste is constituted of a metal powder, a solvent, and a varnish.
Next, the multiple ceramic green sheets with the conductive paste applied thereto are stacked, and subjected to thermocompression bonding to prepare an integrated raw laminate. This raw laminate is subjected to firing to prepare a ceramic laminate. This ceramic laminate has a plurality of internal electrode layers formed therein. The internal electrode layers have certain end surfaces exposed at the external surface of the ceramic laminate.
Next, a conductive paste as a raw material for external electrode layers is applied onto the external surface of the ceramic laminate including the internal electrode layers with the certain end surfaces exposed, and subjected to firing. This conductive paste is constituted of a metal powder, a glass frit, a solvent, and a varnish. Thus, external electrode layers are formed on the external surface of the ceramic laminate, so as to be electrically connected to specific internal electrode layers.
Finally, in order to improve soldering performance, a plating layer is formed on the surfaces of the external electrode layers, if necessary.
During the production process described above, for example, in the case of forming a plating layer on the surfaces of the external electrode layers, ingress of moisture is caused from minute voids which are present in the external electrode layers. In addition, in the case of using a laminated ceramic capacitor as an example of the ceramic body under a high humidity environment, ingress of moisture is also caused from minute voids which are present in the external electrode layers. There is a problem that the moisture due to the ingress from the external electrode layers as described above reaches minute voids at the interfaces between the internal electrode layers and the ceramic layers which are present in the ceramic laminate, thereby causing a decrease in insulation resistance.
Therefore, for example, Japanese Patent Application Laid-Open No. 2001-102247 (hereinafter, referred to as Japanese Patent Application Laid-Open No. 2001-102247) proposes the structure of a chip-type electronic component for solving the problem described above. The chip-type electronic component proposed in Japanese Patent Application Laid-Open No. 2001-102247 has a thick-film base conductor layer and an external terminal electrode of a surface plating layer which are formed on both ends of a rectangular ceramic substrate, and in the chip-type electronic component, the external terminal electrodes are impregnated with a water repellent member. This impregnation suppresses the ingress of moisture into a porous section of the external terminal electrodes even when the chip-type electronic component is left as it is in a humid place. As a result, moisture is prevented from reaching the electronic component body through the surface plating layer and the thick-film base conductor layer.
In addition, for example, Japanese Patent Application Laid-Open No. 2-301113 (hereinafter, referred to as Japanese Patent Application Laid-Open No. 2-301113) proposes the structure of a laminated ceramic electronic component for solving the problem described above, and a method for producing the laminated ceramic electronic component. In the laminated ceramic electronic component proposed in Japanese Patent Application Laid-Open No. 2-301113, defects such as gaps, bores and pinholes in a ceramic laminate or in external electrodes are filled with an inorganic oxide. In addition, the method for producing the laminated ceramic electronic component proposed in Japanese Patent Application Laid-Open No. 2-301113, includes: forming a ceramic laminate or external electrodes on a ceramic laminate; then immersing the ceramic laminate in an organic metal solution such as a metal alkoxide to impregnate defects such as gaps, bores, and pinholes in the ceramic laminate or in the external electrodes with the organic metal; and then decomposing the organic metal into an inorganic oxide by heating. The implementation of this method suppresses ingress of moisture into the gaps or bores described above.
In the structure of the chip-type electronic component described in Japanese Patent Application Laid-Open No. 2001-102247, the external terminal electrodes have the water repellent material remaining. For this reason, in the case of forming a plating layer in a subsequent step, the surfaces of the external terminal electrodes are likely to have a defect caused in plating deposition, and in the case of mounting the chip-type electronic component onto a substrate or the like by soldering, a defect may be caused.
In addition, the structure of the chip-type electronic component described in Japanese Patent Application Laid-Open No. 2001-102247 fails to achieve the effect of suppressing the ingress of moisture into the electronic component body in the case of a small amount of water repellent material remaining in the external terminal electrodes, or has a defect caused in plating deposition in the case of a large amount of water repellent material remaining in the external terminal electrodes. For this reason, it is difficult to control the treatment condition for impregnating the external terminal electrodes with the water repellent member.
On the other hand, in Japanese Patent Application Laid-Open No. 2-301113, the ceramic laminate is immersed in the organic metal solution such as a metal alkoxide to fill defects such as gaps in the ceramic laminate or in the external electrodes with an inorganic oxide. However, this method is not able to fill even nano-level minute voids with the inorganic oxide, and thus produces an insufficient effect of suppressing the ingress of moisture into the voids.